Implantable pump with reservoir level detector

ABSTRACT

An implantable pump includes a base plate and a can that are parts of the pump housing. The base plate bottom divides the housing into a first electronics chamber and a second chamber. A bellows mechanism is connected to the base plate and is disposed within the second chamber. The bellow mechanism has an expandable sidewall and a bottom plate. The bellow mechanism divides the second chamber into a medicament receiving portion and a non-medicament-receiving portion. The bellow mechanism has an intermediate plate disposed within the medicament-receiving portion. A coil is disposed in a recess on the lower surface of the base plate, and the coil is spaced from an internal wall of the recess. The amount of fluid remaining in the implantable pump can be monitored by energizing the coil. A primary magnetic field is generated by the energized coil. A secondary magnetic field, which is dependant on the position of the bottom and intermediate plate of the bellow mechanism, couples back to the primary field affecting the electrical characteristics of the coil. The amount of fluid remaining in the reservoir is determined based on the resulting changes in the electrical characteristics of the coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

The present invention relates to an implantable infusion pump having areservoir level detector. More specifically, the present inventionrelates to an implantable infusion pump having a reservoir with anintermediate plate, which can be used to indicate the amount of fluidremaining within the reservoir.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 6,755,814, which is commonly owned by the assignee of thepresent invention, discloses an implantable infusion pump that has areservoir level detector. The pump includes a housing having a can and abase plate, which base plate bottom divides the housing into a pumpelectronic chamber and a propellant chamber. A bellow mechanism isdisposed within the propellant chamber. The bellow mechanism has a baseor bottom plate. The medicament for delivery to a patient is storedwithin the bellow mechanism. A propellant is disposed about the bellowmechanism within the propellant chamber. The propellant by compressingthe bellow mechanism pushes the medicament out of the bellow mechanismthrough a flow restrictor, a valve and outlet. The bottom of the bellowgets closer to the base plate as the medicament flows out of the bellow.A coil is disposed within a recess in the lower (propellant facing)surface of the base plate. A capacitor is electrically connected to thecoil to form a resonant circuit.

When energized, the coil generates a primary electromagnetic field,which flows through the bottom plate of the bellow mechanism and induceseddy currents therein which intensities increase the closer the bottomplate gets to the coil. The eddy currents generate a secondary magneticfield, which is coupled back to the primary field. The closer the bottomplate is to the coil, the stronger the secondary magnetic field is andits influence on the primary field. This coupling brings about change tothe inductance of the coil and thus brings about a displacement or shiftof the resonance frequency of the resonant circuit depending on thedistance between the coil and the bottom plate. Upon measuring theresonance frequency, which is dependent upon the inductance, one skilledin the art can determine the distance that the bottom plate of thebellow mechanism is from the base plate, which can be used to determinethe volume of medicament remaining within the bellow mechanism.

In the prior art, such as the apparatus disclosed in U.S. Pat. No.6,755,814, the measurement of fluid remaining in the reservoir is onlyaccurate for the last 20 ml of fluid within the bellow mechanism. Atfluid levels greater than about 20 ml and because of the increasingdistance between the coil and the bottom plate at those greater volumes,the measured inductance doesn't vary enough to provide accuratemeasurements. Accordingly, there is a need for an implantable infusionpump where the volume of fluid within the bellow mechanism can bemeasured with a greater degree of accuracy, not only above 20 ml, butalso for the range from 0 to 20 ml. There is also a need for animplantable infusion pump where the volume of fluid within the bellowmechanism can be measured for the entire volume range of the reservoir,including at larger volumes, such as, for example, above 20 ml. There isalso a need for an implantable infusion pump that can detect a leak or avalve blockage within the pump system.

SUMMARY OF THE INVENTION

The present invention provides these and other needs with an implantablepump that has a housing. The housing is comprised of a base plate and acan. The can is attached to the base plate. The base plate bottomdivides the housing into an electronics chamber and propellant chamber.A bellow mechanism is connected to the base plate and is disposed withinthe propellant chamber. The bellow mechanism has an expandable sidewalland a bottom plate. The bellow mechanism divides the propellant chamberinto a medicament receiving portion and a non-medicament receivingportion. The bellow mechanism has an intermediate plate disposed withinthe medicament-receiving portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a graph showing the theoretical simulated inductance versusvolume for a pump in accordance with the present invention as comparedto the theoretical simulated inductance versus volume for a prior artpump;

FIG. 2 is a cross-sectional view of a pump in accordance with thepresent invention;

FIG. 3 is a perspective view of the intermediate plate; and

FIG. 4 is a partial cross-sectional view showing a coil disposed in arecess of the base plate.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1-4, an implantable pump 10 in accordance withthe present invention is illustrated. Pump 10 has a housing 12. Thehousing is comprised of a base plate 14 and a can 13. Can 13 is attachedto the base plate 14. Base plate bottom 14 divides the housing into anelectronics chamber 16 and a propellant chamber 18. A bellow mechanism20 is connected to the base plate 14 and is disposed within thepropellant chamber 18. The bellow mechanism 20 has an expandablesidewall 22 and a bottom plate 24. The bellow mechanism 20 divides thepropellant chamber into a medicament-receiving portion 26 and anon-medicament receiving portion 28. In a currently preferred exemplaryembodiment, portion 28 is a propellant receiving portion 28 so that aforce is applied to the bellows causing the medicament withinmedicament-receiving portion 26 to be delivered to an outlet of pump 10in a manner known to those skilled in the art. Alternatively, the pumpmaybe an active pump, such as, for example, a peristaltic-type pump, andthe medicament in medicament-receiving portion is in fluid communicationwith the peristaltic pump conduit so that medicament frommedicament-receiving portion 26 is delivered to the conduit. In thisembodiment portion 28 may contain no propellant at all or a relativelysmall amount of propellant. The bellow mechanism has an intermediateplate 30 disposed within the medicament-receiving portion 26.

Intermediate plate 30 has at least one through hole 32 therein to permitmedicament to pass there through. In a currently preferred exemplaryembodiment, intermediate plate 30 has four symmetrical through holes 32,as illustrated in FIG. 3. Those skilled in the art will readilyappreciate that numerous other configurations can be used forintermediate plate 30 so long as they have the functionality to practicethe specific embodiment. For example, plate 30 could be in the form of agrid. Plate 30 is preferably made of a biocompatible, non-magneticmaterial, such as, for example, titanium. Plate 30 could also be made ofa combination of materials, such as, for example, a sandwich or layersof different materials, with the outer layer being biocompatible.Intermediate plate 30 is preferably disposed 25% to 50% of the distancefrom the base plate 14 to the bottom plate 24 of bellow mechanism 20 atfree length (e.g., when the bellow is in a stable state during itsmanufacturing). More preferably, intermediate plate 30 is disposed 33%to 40% of the distance from the base plate 14 to the bottom plate 24 ofbellow mechanism 20. In a currently preferred exemplary embodiment,intermediate plate 30 is disposed approximately 40% of the distance fromthe base plate 14 to the bottom plate 24 of bellow mechanism 20. Thus,referring now to FIG. 2, the distance b divided by distance a (i.e.,ratio b/a) is preferably 0.40, or 40%.

A coil 34 is disposed in a recess 36 on the lower surface 38 of baseplate 14. As shown in FIGS. 2 and 4, a μ-metal 40 is disposed betweencoil 34 and base plate 14. This μ-metal 40 acts as a rear shield of thecoil to limit the eddy current in the base plate 14. In addition, coil34 is spaced from the internal wall, which is preferably made oftitanium, by a distance d. Coil 34 is isolated from the medicamentchamber with a biocompatible titanium ring 35.

In a currently preferred exemplary embodiment the pump housing 12 ismade of titanium. In addition, as stated above, intermediate plate 30 isalso preferably made of titanium. The sensitivity in detecting theintermediate plate 30 increases with increasing thickness of plate 30.However, increasing the thickness of plate 30, increases the weight ofthe device and decreases the internal volume of the reservoir in thepump because intermediate plate 30 is disposed within the bellowsreservoir medicament-receiving portion 26. The plate may have athickness ranging from 0.2 mm to 0.7 mm, with 0.5 mm being preferred ina currently preferred exemplary embodiment.

The value of the inductance seen across coil 34 is affected by thelocation of the intermediate plate 30 and bottom plate 24. The resonantfrequency of the circuitry in which the coil 34 is placed is influencedby the inductance across coil 34. The amount of fluid remaining in thereservoir is determined based upon the measurement of the resonantfrequency, which is correlated to the inductance.

Currently pending and commonly owned U.S. patent application Ser. No.11/278,048, filed Mar. 30, 2006, and entitled “Methods and Devices forMonitoring Fluid of an Implantable Infusion Pump” discloses, inter alia,a manner of using a fluid level sensor to monitor the amount of fluid ina reservoir. The disclosure of pending application Ser. No. 11/278,048is hereby incorporated by reference. Referring now to FIG. 1, thepresent inventors theorize that with the current configuration includingthe use of an intermediate plate, the apparatus of the present inventionshould be accurate for the entire volume of the pump up to about 40-45mL of fluid within the bellow mechanism, because the inductance shouldvary sufficiently enough to provide accurate measurements. FIG. 1illustrates the simulated inductance versus volume for a pump inaccordance with the present invention as illustrated by dashed line 42.The inductance ranges can vary with the design of the coil and FIG. 1 isjust intended as illustration. For example, the design of the coil canchange the inductance ranges. Such design variables include the numberof turns of the coil, the wire diameter, the wire material, etc. Thegraph also shows the simulated inductance versus volume for a prior artpump (i.e., a pump not having an intermediate plate) as illustrated byline 44. One can readily see that line 44 plateaus about 20 ml. Thus,for a prior art pump one cannot detect changes in the volume of fluidremaining in the reservoir until the remaining fluid drops below about20 ml. However, in accordance with the present invention, when a 40 mlvolume reservoir is used, the accuracy corresponds to ±5 ml when thereservoir has a total volume between about 20 ml and about 40 ml, and afluid level accuracy corresponding to ±2 ml when the reservoir has atotal volume between about 0 ml and about 20 ml. As illustrated in FIG.1, the use of an intermediate plate not only permits measurement of thevolume of fluid remaining within the reservoir at volumes above 20 ml,but also provides greater accuracy in measurements when the volume isbetween 0 and 20 ml. Line 42 has a Δy of about 0.255 mH from 0 to 20 ml,while line 44 has a Δy of about 0.165 mH from 0 to 20 ml. Because ofthis greater variation in Δy, measurements of the volume remaining inthe reservoir when levels are below 20 ml have a greater degree ofaccuracy than the prior art methods.

In implantable pumps of this type, the medicament exiting the pump has amaximum design flow rate and a programmed flow rate. By measuring thevolume over multiple time periods, the average flow rate can bedetermined If this average flow rate is above or below the programmedflow rate during any measured time period, one can conclude that thereis a malfunction of some sort in the pump. For example, the valve of thepump may be stuck in the open or closed position or the valve may haveweaknesses or intermittent malfunctions. Of course, if the average flowrate is zero, and below the programmed flow rate, then one can concludethat there is a blockage somewhere within the pump. Similarly if theaverage flow rate is the maximum design flow rate and above theprogrammed flow rate, then one can conclude that there is a leak (suchas valve blocked in open state) somewhere in the pump after the flowrestrictor.

It will be understood that the foregoing is only illustrative of theprinciples of the invention, and that various modifications can be madeby those skilled in the art without departing from the scope and spiritof the invention. All references cited herein are expressly incorporatedby reference in their entirety.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. While therehave been shown, described, and pointed out fundamental novel featuresof the invention as applied to a preferred embodiment thereof, it willbe understood that various omissions, substitutions, and changes in theform and details of the devices illustrated, and in their operation, maybe made by those skilled in the art without departing from the spiritand scope of the invention. For example, it is expressly intended thatall combinations of those elements and/or steps, which performsubstantially the same function, in substantially the same way, toachieve the same results are within the scope of the invention.Substitutions of elements from one described embodiment to another arealso fully intended and contemplated. It is also to be understood thatthe drawings are not necessarily drawn to scale, but that they aremerely conceptual in nature. Accordingly, the invention is not to belimited by what has been particularly shown and described, except asindicated by the appended claims. All publications and references citedherein are expressly incorporated herein by reference in their entirety.

1-17. (canceled)
 18. A method of monitoring the amount of fluidremaining in an implantable pump, the pump having a housing; a baseplate connected to said housing, said base plate dividing said housinginto an electronics chamber and a second chamber; a bellow mechanismconnected to said base plate and disposed within said second chamber,said bellow mechanism having an expandable side wall and a bottom plate,said bellow mechanism dividing said second chamber into a medicamentreceiving portion and a non-medicament receiving portion, said bellowmechanism having a intermediate plate disposed within said medicamentreceiving portion; and a coil disposed on the lower surface of the baseplate; the method comprising the steps of: energizing the coil such thata magnetic field is generated by the coil; and determining the amount offluid remaining in the reservoir based on the electrical characteristicsof the coil.
 19. The method of claim 18, further comprising the step of:generating a frequency signal based on the value of the inductance; andmeasuring the value of the frequency.